Just to be clear, psychological disabilities are just as real as a physical handicap. I know I'm picking on your wording, but it's important to acknowledge the truth of the matter in the words we use. Stuttering is a real handicap because stutterers have difficulty doing things non stutterers do with ease, like doing telemarketing work or ordering what we actually want at the drive through. How exactly stuttering works isn't fully understood. It appears to have a genetic component, but at the same time everybody experiences dysfluency to some degree.